Liquid crystal displays (LCDs) provide a flat display in a relatively thin package that is suitable for use in a variety of electronic goods. LCDs are commonly used as screens or displays for a wide variety of electronic devices, including such consumer electronics as televisions, computers, and handheld devices (e.g., mobile phones, audio and video players, gaming systems, and so forth). Further, such LCD devices have also been utilized for digital signage, such as advertisement displays which are generally located outdoors. The LCD devices have become ubiquitous in modern times and are being increasingly installed in both indoor and outdoor environments. These LCD devices are expected to always generate a superior image quality irrespective of the lightning conditions, i.e., whether it is a bright sunny outdoor environment or a dark nightclub environment. Furthermore, these LCD devices are expected to be energy efficient, especially when used in portable handheld devices which are generally powered by batteries with limited energy capacity.
Typical liquid crystal display devices are transmission type, which include a light source, generally a backlight, disposed at the rear or one side thereof. The amount of the backlight from the light source which passes through the liquid crystal display panel is controlled in order to realize an image in the liquid crystal display device. Such transmission type liquid crystal display device is disadvantageous when the environment is bright. When the liquid crystal display device needs to be viewed at a position exposed to direct sunlight or direct illumination light, the display quality is inevitably lower due to the ambient light. That is, the color reproducibility is lower and the display is not sufficiently recognizable because the display light is less bright than the ambient light. For example, when a liquid crystal display device receives direct sunlight or illumination light, surrounding images are mirrored, making it difficult to observe the display itself. In order to improve the display quality under a bright environment, the intensity of the backlight from the light source needs to be increased. This increases the power consumption of the light source and thus the overall power consumption of the liquid crystal display device.
In some cases, reflection type liquid crystal display devices have been used for displays which are often used outdoors. Usually, such a reflection type liquid crystal display device is provided with a reflector formed on one of a pair of substrates in place of the backlight so that ambient light is reflected from the surface of the reflector. However, the reflection type liquid crystal display device using the reflection of ambient light is disadvantageous in that the visibility of the display is generally very low when the surrounding environment is dark, because of the lack of the ambient light to reflect back.
Some known liquid crystal display devices utilize a construction which realizes both transmission of back light as well as reflection of external light for displaying an image. For example, U.S. Pat. No. 7,525,626 discloses a transflective liquid crystal display having a reflector region and a transparent region in one pixel. The said transflective liquid crystal display is able to display using both the light from the backside light source and surrounding light from outside. The transflective liquid crystal display simultaneously uses backside light source and surrounding outside light, as the light sources. Specifically, in a bright place, the surrounding outside light is reflected by the reflector region that is provided in a pixel to a visible side in order to boost brightness for displaying an image.
However, the known liquid crystal display devices utilizing such trans-reflective pixels do not provide any means for controlling transmission regions and reflection regions of the pixels independent to each other. Accordingly, there are no suitable means to regulate such liquid crystal display devices for varying intensity levels of external light to deliver a calibrated image with appropriate brightness each time. The present invention has been made in view of such considerations, and it is an object of the present invention to improve the display quality of such liquid crystal display device.